Capacitor aging



June 16, 1964 e. GIACOMELLO 3,137,058

CAPACITOR AGING Original Filed Jan. 25, 1958 m E INVENTOR Giacomo GLacomeflo ATTORNEY 5 United States Patent fiice 3,137,858 Patented June16, 1964 3,137,058 CAPACITOR AGING Giacomo Giacornello, Milan, Italy,assignor to Sprague Electric Company, North Adams, Mass, a corporationof Massachusetts Original application Jan. 23, 1958, Ser. No. 710,746.Divided and this application Apr. 5, 1961, Scr. No.

1 Claim. (Cl. 29--25.31)

This invention relates to the aging of electrolytic capacitors, moreparticularly to the type of aging that improves the operatingcharacteristics of these capacitors.

In the past it has been the practice for manufacturers of electrolyticcapacitors to subject a capacitor, before or after encasing in thecontainer or envelope in which it is to be used, to the action of anoperating voltage for a period of time in order to lower the leakagecurrent and bring its operating characteristics up to a higher level ofefficiency. It appears that no matter how carefully the capacitor isassembled from its component parts, an anode dielectric film that ispreformed before assembly suffers l significant degradation or damage,probably by reason of the handling it undergoes during assembly. Becausebetter operation of the capacitor can be obtained when the dielectricfilm is madeby electrolytic formation in an electrolyte which isdifferent from that incorporated in the final capacitor when it isplaced in service, it is preferred to first form the dielectric coatingin the desired forming electrolyte, then assemble the formed anode inthecapacitor, then introduce the service electrolyte by "impregnation,and then go through the aging procedure even though it makes themanufacture more complicated.

Among the objects of the present invention is the provision of a novelaging process which simplifies the above manufacture. It is anotherobject of this invention to impregnate electrolytic capacitors duringaging in a manner which effectively removes gas pockets from within thecapacitor and simultaneously provides an effective aging of thecapacitor.

The above as well as additional objects of the present invention will bemore clearly understood from the fol lowingvdeslcription of several ofits exemplifications, reference being made to the accompanying drawingwherein:

FIG. 1 is vertical sectional view of aging apparatus exemplifying thepresent invention; and

FIG. 2 is a modified form of aging apparatus representative of thepresent invention.

According to the present invention, the aging of electrolytic capacitorsections is carried out during the impregnation with an aging potentialapplied to the electrodes of the section. The aging potential is appliedwith a very high current density as the potential is applied along thefoil with the progressing electrolyte. Also the effect of producing gason the anode and cathode during the aging is minimized by thisinvention. Bubbles form as a result of the gas production and ordinarilytend to prevent further aging. This invention provides for andfacilitates their removal.

One highly effective techique for carrying out the process of thepresent invention is to wind a set of capacitor electrode foils withporous spacer ribbons to make an electrolytic capacitor section,connecting terminal leads to at least the anode electrode foil, applyingto the foils an electric potential that renders the anode foil positivewith respect to at least one other foil, at least one other electrodewhich need not be a foil and may be the container, and impregnating thewound section with an electrolytic capacitor electrolyte while thepotental is applied so as to age the section during the impregnation.

FIGURE 1 shows an arrangement by which pneumatic forces are so utilized.In this modification an evacuating chamber is provided with an exit line82 connected to a source of suction. A valve 84 in this line controlsthe application of the suction to the interior of the chamber. A lid 86suitably sealed against air leakage as by gasket 88, provides access tothe interior of the chamber for insertion and removal of the capacitorsections to be impregnated. Electric supplyleads 89, 90 are arranged topass through the lid on one side of which they are connected to thecapacitor sections and on the other side of which to the source ofelectric power. Chamber 80 is provided wtih an impregnating line 92valved as at 94 and extending to near the bottom of anelectrolyte supplycontainer 96.

The apparatus of FIGURE 1 is used by loading the capacitor sectionssuitably connected to the leads 89, 90 into the chamber 80, placing asuitable amount of service electrolyte in container 96;, closing valve94, and opening valve 84 to apply suction so as to evacuate the chamber.After reducing the pressure in this chamber to about 10 millimeters ofmercury or less, valve 94 is opened and the supply of electric power toleads 89, 90 commences. The suction in the chamber draws the electrolyte up into it, and the capacitor sections in this way become immersed.Because of the preliminary evacuation, the electrolyte more readilypenetrates into all voids in the sections.

The section is positioned with its axis in a horizontal radialorientation for the reception of the electrolyte. As indicated above,the electrolyte as it progresses into the section is proceedinglaterally of the chamber. In its impregnation of the section theelectrolyte carried a high current density along the foil. This providesa higher current density for the few seconds that the advancingelectrolyte passes along each area of the foil while wetting the foilthan would be possible with the normal application of the agingpotential to the foil area of the anode. At thesame time it is a featureof this combined impregnation and aging that the current drops offrapidly along the electrode and consequently a large power supply is notnecessary in attaining the effects of this invention. It is also to benoted that the elimination of bubbles is assisted. These bubbles resultfrom the gas produced at the electrodes and tend to reduce the agingeffect of the aging potential.

The pressure in the chamber 80 above the drawn-in electrolyte can beincreased at atmospheric or above either immediately upon immersion, orafter a delay of 5 to 10 minutes. Only about 15 minutes of immersionwill give properly impregnated and aged capacitors whether or not thepressure above the electrolyte is raised at atmospheric. When theelectrolyte is relatively viscous, such as at lower temperatures, it maybe desirable to repeat the impregnation, as by draining the electrolyte,again applying suction, and after the pressure is reduced, againpermitting the electrolyte to be sucked up so as to immerse thesections.

FIGURE 2 shows a further embodiment of the aging invention with adifferent assistance means in which the impregnation is accelerated bymeans of the forces developed through compressional vibration. Animpregnation receptacle 102 is here illustrated as having its floorprovided with a supersonic vibrator 102. A group of capacitor sectionswith their terminal leads connected together and to a source of electricpower by means of connectors 104, 105, are placed in the receptacle, anda quantity of service electrolyte 107 introduced to cover the sections.The vibrator is then operated at a frequency of 20 to 50 thousand cyclesper second under which conditions an electrolyte having a viscosity of30 centistokes, and a density of 1.1 grams per cubic centimeter, willthoroughly impregnate and age capacitor sections with the application ofas little as 10 Watts of vibrational energy per quart of impregnant. Inthis method the removal of gas in the form of bubbles is largelyassisted by the vibrational treatment of the! capacitor sections duringthe impregnation.

The aging as described above is useful with capacitor sections havingaluminum anodes covered with in situ formed oxide film provided as inthe above mentioned Scherr et al. application or by the use of anodicoxidation of aluminum foil that is etched with unvarying direct cunent,or even the oxidation of unetched foil. Suitable oxidizing electrolytefor this formation are disclosed in U.S. Patent No. 2,444,725 issuedJuly 6, 1948.

Tantalum can also be used in place of aluminum as the anode material andcan be provided in the form of foils also oxidize anodically as in themanner indicated in the U.S. Patent No. 2,739,110. Columbium is anothersuitable anode material.

The capacitors aged in accordance with the present invention can have 1,2, 3, 4 or more anodes separately assembled with one or more cathodes,and the cathodes can be in the form of foils or can be for the purposeof aging in any other form such as the walls of a container which formsthe casing for the capacitors or of the impregnating vessel. Whereseparate anodes are used they can all'be aged simultaneously bysupplying all with current having the proper potentials with respect toone or more of the cathodes. It is also possible that in constructionshaving more than one cathode, only one need be connected in the agingcircuit with all the anodes in order to reduce the number of terminalconnection operations.

The aging potential should be less than the forming potential and higherthan the designed operating potential. The forming potential is usuallyfrom to percent greater in value than the operating potential but may beas much as 50 percent higher than the operating potential. Where theaging current is applied at a potential of about 25 percent higher thanthe design operating potential, the aging is not fully effective, eventhough the aging is prolonged in duration. Such low voltage aging can beused, however, where minimum leakage current is not important, and forsuch purposes the low voltage aging can also be terminated at the end ofthe impregnation. Aging at a voltage more than 50 percent greater thanthe design operating voltage is generally to be avoided inasmuch as itchanges the characteristics of the initially formed coating.Furthermore, extremely high voltages can also cause localized breakdownof the dielectric coatmg.

The impregnation temperature is generally as high as convenient. It ispreferred to use temperatures of at least about 100 C., inasmuch as theviscosity of the impregnant is thereby reduced sharply, and more perfectimpregnation takes place very rapidly. However, any impregnationtemperature can be used even down to 0 C. if desired, particularly withcapacitor sections that have will elfect impregnation, but impregnationin this way is likely to be incomplete unless continued for at leastthree or four hours. The aging will also be incomplete unless carriedout for at least about 15 minutes during the completion of theimpregnation. The eifect of applying a very high current density as theelectrolyte progresses along the foil is achieved with either type ofimpregnation. It is achieved more rapidly with the impregnation atreduced viscosities at a pressure differential. It thus appears that theimpregnation assistance means while having common attributes aredesirable in character. Similarly, the removal of inhibiting gas bubblesis more effectively achieved with the pressure differential and atreduced electrolyte viscosities.

The internal construction of the capacitor sections to be impregnated inaccordance with the present invention can be varied in any desiredmanner. For example, the spacers can project from both sides of aconvolutely Wound assembly, and can also be extra long so that a fewturns of spacer are wrapped around the section.

- The electrical connections supplying the aging current are alsosubject to Wide variation.

. This invention relates to aging electrolytic capacitors beforeintroduction into service in combination with impregnation of thecapacitors in such a manner as to assist the aging. The unique andunexpected characteristics and combination of characteristics have beendescribed and illustrated herein in both general and specific terms. Inthe description it is intended to provide a better understanding of theinvention and its aspects without limiting the invention and withoutsuggesting an equivalency between various combined features.

This application is a division of my c0pending application Serial No.710,746 filed January 23, 1958, now abandoned.

What is claimed is:

The process of making an electrolytic capacitor which comprises thestepsof convolutely winding a set of capacitor electrode foils having atleast one formed anode v foil with porous spacer ribbons to create acapacitor sec tion, connecting a terminal lead to 'at least said anodefoil, positioning said capacitor section in a container with a liquidelectrolyte compound therein, applying to at least said anode foil ofsaid capacitor section an electrical potential with a high currentdensity that renders the foil positive with respect to a cathode,vibrating said capacitor section by a supersonic vibration, acceleratingthe compound in circulation in contact with said section by vibra-References Cited in the file of this patent UNITED STATES PATENTSCompton June 13, 1944 Brennan Feb. 5, 1946

